Lignocellulosic composites are made from small pieces of cellulosic materials that are bonded together using adhesives. In general, wood or other lignocellulosic materials are first processed to yield veneers, strands, fibers and chips. Adhesives are then added to the lignocellulosic materials. The resultant mixture is consolidated using pressure and heat to yield a lignocellulosic composite.
Oriented strand board (OSB) parallel strand lumber (PSL), laminated strand lumber (LSL) and softwood plywood (SWPW) are commonly bonded with thermosetting phenol formaldehyde (PF) or phenol resorcinol formaldehyde (PRF), commonly called “phenolic” resins. The phenolic resins provide excellent wet durability. Particleboard (PB), medium density fiberboard (MDF), hardboard and hardwood plywood (HWPW) have traditionally been bonded with urea formaldehyde. Urea formaldehyde can hydrolyze to produce formaldehyde emissions over the life of the product. Due to increased concern over long term formaldehyde emissions, much of the North American HWPW industry has turned to either soy-based adhesives or polyvinyl acetate (PVAc) as alternative adhesives. Several PB and MDF manufacturers have switched to polymeric methylene diphenyl diisocyanate (pMDI) adhesives as a no-added formaldehyde option.
The adhesives used to bond lignocellulosic materials typically have limited fire resistance and tend to burn as readily as the lignocellulosic substrate. To improve fire resistance, various fire resistant coatings and paints can be applied onto lignocellulosic composites. However, these fire resistant coatings and paints add significant cost and require additional processing steps. Furthermore, these fire resistant coatings and paints can crack and spall thereby reducing fire resistance properties. Fire resistant coatings and paints can employ magnesium oxychloride cements (MOC), which can suffer from poor water resistance. Prolonged exposure of MOC's to water often reduces adhesion between the cement crystals. These drawbacks have significantly limited the use of MOC compounds for lignocellulosic composites.